Breast cancer incidence has increased substantially during the last three decades, coinciding with the introduction of hormone mimics into the environment. It has been postulated that developmental exposure to xenoestrogens and in particular to bisphenol-A (BPA) may be the causal agent underlying this increase. It is hypothesized that BPA administered throughout the prenatal period (beyond gestational day 9) and postnatal period (birth to postnatal day 21) alters the expression of estrogen-responsive genes through estrogen receptor mediated mechanisms and/or by affecting DNA methylation, which in turn results in altered mammogenesis leading to an increased susceptibility to breast cancer. The following Specific Aims will be pursued: Aim 1: To determine the levels at which BPA exposure results in an increased incidence of mammary cancer. Two windows of susceptibility will be examined: from gestational day (GD) 9 to birth, and from GD9 to weaning (postnatal day [PND21]). At 50 days of age, rats will be challenged with a single intraperitoneal dose of the carcinogen nitrosomethylurea (NMU, 20 mg/kg) or vehicle. Tumor incidence and latency period will be measured (n=30 rats/group for an a level of 0.05 and power=0.80). The time-course of histoarchitectural changes and emergence of pre-neoplastic and neoplastic lesions will be examined. To assess the internal dose, BPA levels in blood of dams will be measured during the exposure period. Additionally, a marker of exposure will be developed to increase the range of detected doses. Aim 2: To explore mechanisms responsible for the induction of neoplastic changes due to BPA exposure. The genesis and maintenance of tissue architecture involves several levels of biological organization. Thus, this study will explore i) BPA exposure effects on mRNA expression, ii) the methylation pattern of genomic DNA both in the stroma and epithelium, and iii) the role of stromal and epithelial alterations by means of tissue recombination experiments and whether the presence of pre-neoplastic lesions is due to BPA-mediated stromal and/or epithelial alterations. This work will immediately and significantly impact: 1) Basic science: The unraveling of the morphogenic events that mediate the carcinogenic effect of BPA will signal the central role of tissue architecture in carcinogenesis, and thus switch the focus of research in cancer from events occurring at the subcellular level of organization to the tissue level of organization and to non-mutagenic agents, such as morphogens and hormones, as important causal agents. 2) Public policy: It will provide two essential pieces needed for risk assessment of BPA: unequivocal evidence of the carcinogenic potential of environmentally relevant BPA exposure in the mammary gland, and measurements of internal dose needed to compare animal with human exposures. 3) Medical Practice: It will make physicians aware of environmental pollution as a cause of diseases, particularly when dealing with cancers in hormone-target organs. PUBLIC HEALTH RELEVANCE: Perinatal exposure to xenoestrogens such as BPA is associated with the increase in deleterious health effects observed in human populations during the last fifty years, including breast cancer, infertility and obesity. We observed that animals exposed perinatally to low doses of BPA developed mammary precancerous lesions. The proposed study aims at identifying the association between perinatal exposure to BPA and mammary tumors and characterizing the underlying mechanisms. This is of utmost relevance to the evaluation of BPA, a widespread contaminant found in 92% of the tested American population and therefore it has the potential to greatly impact public health and public health policy.